Numerical Study On Buckling Behavior Of Double-walled Carbon Nanotubes With Intramolecular Junctions

Carbon nanotubes (CNTs) have attracted considerable attention from scientists and researchers since their discovery in 1991 by Iijima and have shortly become an important member of nano-materials. Carbon nanotubes can be metallic or semiconducting depending on their chirality, which makes them function as structural elements for nano-scale electronic devices. However, the application of carbon nanotubes requires two arbitrary tubes seamlessly fuse together like water pipes according to certain rules. The simplest way is via a pair of pentagon-and-heptagon (5-7) in the otherwise "ideal" carbon nanotubes to form an intramole-cular junction(IMJ). The electrical properties of IMJ can be different depending on the composition of IMJ's two tubes which makes the potential usage of IMJ as rectifier diodes in the circuit, switches, etc. Owing to the large aspect ratio and the hollow tubular structure, nanotubes are susceptible to buckling and structural instability under loads, and it makes sense that necessary work should be directed towards the buckling behavior of nanotubes.This paper focuses on the buckling behavior of double-walled carbon nanotubes with intramolecular junctions (DWIMJs) under axial compression load, related work includes analysis modeling and numerical simulation, etc. Molecular dynamics approach is performed to investigate the factors, such as strain rate, length of DWIMJs, temperature, van der Waals force and defect of pentagon-heptagon pair influencing the compressive buckling behavior of DWIMJs. In addition, the length of DWIMJs impacting the compressive buckling behavior of DWIMJs is also discussed via molecular structural mechanics approach.The 3-body Tersoff interatomic potential and Lennard-Jones potential are used in the molecular dynamics analysis to describe the interaction within the chemical bonds between atoms and the long range van der Waals interaction between adjacent layers of the DWIMJs. The molecular structural mechanics model is developed by making the double-walled hollow cylindrical tube equivalent to double-walled space frame structure. Three different finite element models are established, by using beam elements mimic covalent bonds and the van der Waals force is simulated by nonlinear elements. Both eigenvalue buckling analysis and nonlinear ultimate load analysis are executed on tubes.Strain rate, length of DWIMJs, temperature, van der Waals force and defect of pentagon-heptagon pair impacting the critical compressive strain and buckling modes of DWIMJs under axial compressive load are considered in molecular dynamics analysis, also figures illustrating the relationship between strain rate and the factors, strain rate and typical buckling modes are also given.The compressive buckling behavior of DWIMJs with different tube lengths are mainly analyzed under molecular structural mechanics approach. The results indicate that, the critical compressive strain decreases with the increase of the tube length, either in the eigenvalue buckling analysis or in the nonlinear ultimate load analysis. When the buckling mode is column buckling, the results of molecular structural mechanics method agree well with the data under molecular dynamics simulation; Otherwise the buckling mode is shell buckling, finite element method can not accurately reveal the trends of the buckling strain with respect to the tube length.